A developing device including a developing roller and a developer layer forming member for forming a layer of a one component developer on the roller. The developing device satisfies the relationships (1) 20Q/M>13.1.alpha.-44.5, wherein X represents the ratio (% by weight) of the wax present on the surface of the developer to the total of the wax therein; .alpha. represents the angle formed by a tangent line to the member at a point B, which is the center of the contact zone of the member contacted with the roller, and another tangent line at a point A thereof 0.5 mm apart from the point B toward the tip of the member, wherein .alpha. is 0 to .pi./2 radian; and Q/M represents the charge quantity (.mu.C/g) of the toner per unit weight.